1. Field of the Invention
The present invention relates to a super-compact motor.
2. Related Background Art
Among compact motors, there is a compact cylindrical stepping motor as shown in FIG. 15.
In FIG. 15, a motor as shown includes two stators 102 arranged in an axial direction, and each stator has two stator yokes 106 opposed to each other in the axial direction. For each stator 102, a stator coil 105 is coaxially wound around a bobbin 101 held by two stator yokes 106. Each bobbin 101 on which the stator coil 105 is wound is pinched between and secured by two stator yokes 106 from the axial direction. Each stator yoke 106 is provided with stator teeth 106a, 106b arranged alternately. On the other hand, a pair of stator yokes 106 having stator teeth 106a, 106b are secured to a case 103 of each stator 102. In this way, the stators 102 are constructed.
A flange 115 and a bearing 108 are secured to one (left one) of two cases 103, and an opposite bearing 108 is secured to the other case 103. A rotor 109 has a construction in which a rotor magnet 111 is secured to a rotor shaft 110. Air gaps are defined between an outer peripheral surface of the rotor magnet 111 and inner peripheral surfaces of the stator yokes 106 of the stators 102. The rotor shaft 110 is rotatably supported by two bearings 108 secured to the cases 103.
FIG. 17 is a plan view of a stepping motor for driving a single coil such as used in a watch and the like. In FIG. 17, the reference numeral 201 denotes a stator comprised of a permanent magnet; numerals 202, 203 denote stators: and numerals 204 denote a coil.
However, in the conventional compact stepping motor shown in FIG. 15, since the cases 103, bobbins 101, stator coils 105 and stator yokes 106 are concentrically arranged around the rotor, the entire dimension of the motor becomes great. Further, as shown in FIG. 16, since magnetic flux generated by energization of the stator coil 105 mainly passes through an end face 106a1 of the stator tooth 106a and an end face 106b1 of the stator tooth 106b, the magnetic flux does not act on the rotor magnet 111 effectively, with the result that high output of the motor cannot be obtained.
Also regarding the motor shown in FIG. 17, magnetic flux generated by energization of the coil 204 is concentrated into the smallest gap between the rotor 201 and the stator 202 and does not act on the magnet effectively.
The inventors have proposed a motor solving the disadvantage of the conventional motor shown in FIG. 15, as disclosed in U.S. Pat. No. 5,831,356.
In this proposed motor, a cylindrical rotor comprises permanent magnets equidistantly disposed in a circumferential direction and having alternate magnetic poles; a first coil, a rotor and a second coil are sequentially disposed in an axial direction of the rotor; a first outer magnetic pole and a first inner magnetic pole, which are excited by the first coil, are opposed to outer and inner peripheral surfaces of the rotor and a second outer magnetic pole and a second inner magnetic pole, which are excited by the second coil, are opposed to the outer and inner peripheral surfaces of the rotor; and a rotary shaft (rotor shaft) is extended from the interior of the cylindrically arranged permanent magnets.
Although such a motor can have high output and small outer dimension, since the diametrical dimensions of the inner magnetic poles are small, it is difficult to manufacture magnetic teeth. Further, it has been requested that stable output having no vibration be obtained from a motor having a small diametrical dimension.
To this end, the inventors have recently proposed a motor in which inner magnetic poles have a configuration having good workability, as described in U.S. patent application Ser. No. 08/994,994, and also proposed a rotor in which output transmitting means, such as a gear or a pulley, can easily be attached to a rotary shaft having a small diametrical dimension and stable output having no vibration can be obtained, as described in U.S. patent application Ser. No. 09/022,474.
Recently, it has been requested to provide a motor having high output and super-compact size.
To this end, the inventors have recently proposed a motor constructed as a single phase motor to achieve high output and super-compact size, as described in U.S. patent application Ser. No. 09/293,063.
In recent years, it has been requested that such a motor having high output and super-compact size made be further highly accurate.